1,4-Dihydro-2,6 dimethylyridine-3,5-dicarboxylic acid ester compositions

ABSTRACT

Stabilization of chlorine-containing thermoplasts with 1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylic acid esters alone or, in particular, together with a metal-containing stabilizer as synergist.

This is a divisional of application Ser. No. 958,760, filed on Nov. 8,1978, now U.S. Pat. No. 4,214,088, issued July 22, 1980.

The present invention relates to new stabilisers, and also to their useon their own or particularly together with synergists, for stabilisingchlorine-containing thermoplasts.

It is known that stabilisers can be added to chlorine-containingthermoplasts, for example, polyvinyl chloride, in order to reduce damageand/or discoloration in the substrate caused by exposure to heat.

The known effective thermostabilisers include for example organic metalcompounds of magnesium, calcium, strontium, barium, zinc, cadmium, tin,lead and antimony. Also mixtures of some of these compounds are known.

There are however also mentioned in patent literature numerousmetal-free thermostabilisers for chlorine-containing thermoplasts. Onlya small number of products however satisfy technical requirements andare actually used, or example esters of aminocrotonic acid,diphenylthiourea and α-phenylindole. But these too have unfavourableproperties, such as insufficient inherent stability and a tendency todecompose at the processing temperature, and/or high volatility and/orpoor compatibility with the substrate, and/or lacking stability tolight.

Good stable stabilisers which do not have the above mentioneddisadvantages are known however from the German Offenlegungsschrift No.2,436,007. These are compounds of the formula ##STR1## in which R is ahydrocarbon radical, for example an alkyl, cycloalkyl or phenyl group.These stabilisers do indeed induce a good degree of stabilisation over ashort period, but are somewhat weaker with regard to longtermstabilisation.

It has now been found that a surprisingly better longterm stabilisationis obtained by using alkoxyalkanol diesters or alkylmercaptoalkanoldiesters of 1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylic acid.

The subject matter of the present invention is accordingly a stabiliserof the formula (I) ##STR2## in which R is branched-chain orstraight-chain C₁ -C₂₀ alkyl, X is sulfur or oxygen, and p denotes thenumbers 1-8 inclusive.

Preferred stabilisers are those of the formula (II) ##STR3## in which pdenotes the numbers 1-4 inclusive, particularly 2 and 3, and q denotesthe numbers 1-11 inclusive, especially 11.

It has likewise been found that the simultaneous use of a diester of1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylic acid and of astabiliser containing a metal from the group comprising barium, cadmium,tin or antimony, or also zinc combined with at least one of theaforementioned metals, has a surprisingly strong synergistic effect,that is to say, an effect greater by far than the additivethermostabilising effect to be expected in such a case.

A further subject matter of the present invention is therefore astabiliser mixture consisting of

(a) a dicarboxylic acid diester of the formula (III) ##STR4## in whichR₁ is branched-chain or straight-chain C₁ -C₂₀ alkyl, C₅ -C₇ cycloalkylor phenyl, or a group of the formula --(CH₂)_(p) --X--R wherein X issulfur or oxygen, R is branched-chain or straight-chain C₁ -C₂₀ alkyl,and p denotes the numbers 1-8 inclusive; and

(b) a stabiliser containing a metal from the group comprising barium,cadmium, tin or antimony, or also zinc combined with at least one of theaforementioned metals.

R and R₁ as C₁ -C₂₀ alkyl are straight-chained or branched-chain C₁ -C₁₂alkyl, especially straight-chain C₁ -C₁₂ alkyl. Examples are: methyl,ethyl, propyl, isopropyl, butyl, tert-butyl, n-pentyl, α-methylpentyl,hexyl, 2,4-dimethylpentyl, octyl, 6-methylheptyl, 2-ethylhexyl, decyl,dodecyl, octadecyl, octadecylethyl and eicosyl. As alkyl, R₁ ispreferably C₁ -C₄ alkyl, particularly ethyl and also especially dodecyl;and R is preferably dodecyl.

R₁ is C₅ -C₇ cycloalkyl is cyclopentyl, cycloheptyl and particularlycyclohexyl.

For the synergistic stabiliser mixture are preferred dicarboxylic aciddiesters of the formula (III) in which R₁ is a group --(CH₂)_(p) --X--Rhaving the above-given meaning, and particularly a group --(CH₂)_(p)--S--(CH₂)_(q) --CH₃ in which p denotes the numbers 1-4 inclusive,especially 2 and 3, and q denotes the numbers 1-11 inclusive,particularly 11.

Metal-containing stabilisers used are Ba/Cd-, Ba/Zn-, Ba/Cd/Zn- andpreferably organotin-stabilisers. They are therefore in particularmixtures of Ba-, Cd- and/or Zn-stearates or -carboxylates, ororganotin-mercaptides or -maleates, such as are described for example inPure and Appl. Chem., Vol. 49, pp. 627-648, Pergamon Press, 1977 (H. O.Wirth, H. Andreas, The Stabilisation of PVC against Heat and Light).

The metal-containing stabilisers to be used according to the inventionare generally known, and they are already being used at times forstabilising chlorine-containing thermoplasts.

1,4-Dihydro-2,6-dimethylpyridine-3,5-dicarboxylic acid diesters of theformula (I) are new, and they can be produced both by a new processaccording to the following equation ##STR5## and by processes alreadyknown, for example (a) by the of Hantzsch process (Org. Synth., Coll.Vol. II, pp. 214 and 215), in which acetoacetic ester is reacted withformaldehyde and ammonia; or

(b) by reaction of Urotropin with ammonium acetate (GB PatentSpecification No. 1,294,650).

The process (a) is a two-stage process and requires relatively longreaction times, whereas process (b) is similar to the new processmentioned above, both being single-stage processes requiring only shortreaction times.

Stabilisers of the formula (III) in which R₁ is alkyl, cycloalkyl orphenyl are already known from the German Offenlegungsschrift No.2,436,007. They can all be produced by any one of the three processesgiven above.

German Offenlegungsschrift No. 2,436,007 mentions however onlystabilisers of the formula (III) in which R₁ as alkyl is C₁ -C₈ alkyl.It has however now been found that the stabilisers of the formula (III)in which R₁ is dodecyl surprisingly induce an even higher degree ofstabilisation.

Further subject matter of the present invention is accordingly thestabiliser 1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylicacid-dilauryl ester.

The stabiliser according to the invention, and particularly thesynergistic stabiliser mixture according to the invention, areexcellently suitable for providing protection against heat-induceddegradation of chlorine-containing thermoplasts.

Still further subject matter of the present invention is therefore astabilised composition comprising a chlorine-containing thermoplasticpolymer and, as stabiliser, 0.5-2.5% by weight, preferably 1-2% byweight, of the dicarboxylic acid diester of the formula (I), orpreferably a stabiliser mixture of 0.5-2.5% by weight, preferably 1-2%by weight, of the dicarboxylic acid diester of the formula (III) and0.05-1.5% by weight, preferably 0.2-0.5% by weight, of themetal-containing stabiliser, relative to the total composition.

The individual constituents of the stabiliser mixture are incorporated,either separately or already mixed together, into the thermoplasts,which are to be stabilised, before processing in the customaryapparatus.

Chlorine-containing thermoplasts which may be mentioned are:polyvinylidene chloride and preferably polymers formed from or based onvinyl chloride. Preferred are suspension polymers and polymers producedby bulk polymerisation, and also emulsion polymers washed free fromemulsifiers. The polyvinyl chloride can be that containing plasticisersor it can be rigid PVC.

Comonomers for thermoplasts based on vinyl chloride which may bementioned are: vinilidene chloride, transdichloroethane, ethylene,propylene, butylene, maleic acid, acrylic acid, fumaric acid or itaconicacid.

Depending on the purpose for which the moulding compound is to be used,there can be incorporated, before, during or after the addition of thestabiliser or stabiliser mixture according to the invention, furtheradditives, such as lubricants, preferably montan waxes or glycerolesters, fillers, reinforcing fillers such as glass fibres, modifierssuch as additives for increasing impact strength, and/or pigments.

Preferred co-additives are light stabilisers, particularly UVstabilisers, which are added generally in amounts of 0.001 to 2% byweight, relative to the total composition. Suitable light stabilisersand UV stabilisers are for example:

2-(2'-Hydroxyphenyl)-benzotriazoles, for example the5'-methyl-3',5'-di-tert-butyl-, 5'-tert-butyl-,5'-(1,1,3,3-tetramethylbutyl)-, 5-chloro-3',5'-di-tert-butyl-,5chloro-3'-tert-butyl-5'-methyl-, 3'-sec-butyl-5'-tert-butyl-,3'-α-methylbenzyl-5'-methyl-, 3'-α-methylbenzyl-5'-methyl-5-chloro-,4'-hydroxy-, 4'-methoxy-, 4'-octoxy-, 3',5'-di-tert-amyl-,3'-methyl-5'-carbomethoxyethyl- and5chloro-3',5'-di-tert-amyl-derivative.

2,4-Bis-(2'-hydroxyphenyl)-6-alkyl-s-triazines, for example the6-ethyl-, 6-heptadecyl- or 6-undecyl-derivative.

2-Hydroxybenzophenones, for example the 4-hydroxy-, 4-methoxy-,4-octoxy-, 4-decyloxy-, 4-dodecyloxy-, 4-benzyloxy-, 4,2',4'-trihydroxy-or 2'-hydroxy-4,4'-dimethoxy-derivative.

1,3-Bis-(2'-hydroxybenzoyl)-benzenes, for example1,3-bis-(2'-hydroxy-4'-hexyloxy-benzoyl)-benzene,1,3-bis-(2'-hydroxy-4'-octyloxy-benzoyl)-benzene or1,3-bis-(2'-hydroxy-4'-dodecyloxy-benzoyl)-benzene.

Esters of unsubstituted or substituted benzoic acids, for examplephenylsalicylates, octylphenylsalicylate, dibenzoylresorcin,bis-(4-tert-butylbenzoyl)-resorcin, benzoylresorcin,3,5-di-tert-butyl-4-hydroxybenzoic acid-2,4-di-tert-butylphenyl ester or-octadecyl ester or -2-methyl-4,6-di-tert-butylphenyl ester.

Acrylates, for example α-cyano-β,β-diphenylacrylic acid-ethyl ester or-isooctyl ester, α-carbomethoxy-cinnamic acid methyl ester,α-cyano-β-methyl-p-methoxy-cinnamic acid methyl ester or -butyl ester orN-(β-carbomethoxyvinyl)-2-methylindoline.

Nickel compounds, for example nickel complexes of2,2'-thio-bis-[4-(1,1,3,3-tetramethylbutyl)-phenol], such as the 1:1- or1:2-complex, optionally with additional ligands such as n-butylamine,triethanolamine or N-cyclohexyl-di-ethanolamine, nickel complexes ofbis-[2-hydroxy-4-(1,1,3,3-tetramethylbutyl)-phenyl]-sulfone, such as the2:1-complex, optionally with additional ligands such as 2-ethylcapronicacid, nickel-dibutyldithiocarbamate, nickel salts of4-hydroxy-3,5-di-tert-butylbenzyl-phosphonic acid-monoalkyl esters, suchas of methyl, ethyl or butyl ester, or nickel complexes of ketoximes,such as of 2-hydroxy-4-methylphenylundecylketonoxime,nickel-3,5-di-tert-butyl-4-hydroxybenzoate ornickel-isopropylxanthogenate.

Sterically hindered amines, for example4-benzyloxy-2,2,6,6-tetramethylpiperidine,4-stearoyloxy-2,2,6,6-tetramethylpiperidine,bis-(2,2,6,6-tetramethylpiperidyl)-sebacate or3-n-octyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4,5]decan-2,4-dione.

Oxalic acid diamides, for example 4,4'-di-octyloxyoxanilide,2,2'-di-octyloxy-5,5'-di-tert-butyl-oxanilide,2,2-didodecyloxy-5,5'-di-tert-butyl-oxanilide,2-ethoxy-2'-ethyl-oxanilide, N,N'-bis-(3-dimethylaminopropyl)-oxalamide,2-ethoxy-5-tert-butyl-2'-ethyloxanilide and mixtures thereof with2-ethoxy-2'-ethyl-5,4'-di-tert-butyl-oxanilide, or mixtures of ortho-and para-methoxy- as well as of o- and p-ethoxy-disubstitutedoxanilides.

Compared with the stabilisers described in the GermanOffenlegungsschrift No. 2,436,007, the stabilisers of the formula (I)according to the invention induce a better longterm stabilisation.

The stabiliser mixture according to the invention ensures an excellentthermostabilising action which exceeds by far that of the individualcomponents.

The following Examples serve to further illustrate the invention. Theterm `parts` denotes parts by weight, and percentages are percent byweight.

PRODUCTION EXAMPLES Example A1,4-Dihydro-2,6-dimethylpyridine-3,5-dicarboxylic acid-diethyl ester

A mixture of

13.0 g (0.1 mol) of acetoacetic acid ethyl ester,

4.3 g of formalin (corresponding to 0.05 mol of formaldehyde),

3.9 g (0.05 mol of ammonium carbaminate,

85.0 ml of isopropanol, and

15.0 ml of water,

is heated for 20 minutes at 80° C. After cooling, and concentration byevaporating off the solvent, the1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylic acid-diethyl estercrystallises out.

    ______________________________________                                        yield:       9.9 g (78% of theory),                                           melting point:                                                                             182-187° C.,                                              analysis:    % C         % H         % N                                      found:       61.7        7.7         5.6                                      calculated:  61.6        7.6         5.5                                      ______________________________________                                    

Example B 1,4-Dihydro-2,6-dimethylpyridine-3,5-dicarboxylicacid-di-(2'-ethylthioethyl) ester

If the procedure is carried out as in Example A with the singleexception that the acetoacetic acid ethyl ester is replaced with 19.0 g(0.1 mol) of acetoacetic acid-(2-ethylthioethyl) ester, there isobtained the 1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylicacid-di-(2'-ethylthioethyl) ester.

    ______________________________________                                        yield:      14.4 g (77% of theory)                                            melting point:                                                                            102-104° C.                                                analysis:   % C       % H       % N     % S                                   found:      54.3      7.1       3.6     17.1                                  calculated: 54.7      7.3       3.8     17.2                                  ______________________________________                                    

Example C 1,4-Dihydro-2,6-dimethylpyridine-3,5-dicarboxylicacid-di-(2'-laurylthioethyl) ester

If the procedure is carried out as in Example A with the sole exceptionthat the acetoacetic acid-ethyl ester is replaced with 33.1 g (0.1 mol)of acetoacetic acid-(2-laurylthioethyl) ester, there is obtained the1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylicacid-di-(2'-laurylthioethyl) ester.

    ______________________________________                                        yield:      23.2 g (71% of theory)                                            melting point:                                                                            92-94° C.                                                  analysis:   % C       % H       % N     % S                                   found:      68.2      10.6      2.1     10.0                                  calculated: 67.9      10.3      2.1      9.8                                  ______________________________________                                    

Example D 1,4-Dihydro-2,6-dimethylpyridine-3,5-dicarboxylicacid-di-(3'-laurylthio-n-propyl) ester

If the procedure is carried out as in Example A with the sole exceptionthat the acetoacetic acid ethyl ester is replaced with 20.4 g (0.1 mol)of acetoacetic acid-(3-laurylthio-n-propyl) ester, there is obtained the1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylicacid-di-(3'-laurylthio-n-propyl) ester.

    ______________________________________                                        yield:      24.2 g (70% of theory)                                            melting point:                                                                            87-90° C.                                                  analysis:   % C       % H       % N     % S                                   found:      68.2      10.0      2.2     9.2                                   calculated: 68.7      10.5      2.1     9.4                                   ______________________________________                                    

Example E 1,4-Dihydro-2,6-dimethylpyridine-3,5-dicarboxylicacid-di-(2'-ethoxyethyl) ester

If the procedure is carried out as in Example A with the sole exceptionthat the acetoacetic acid ethyl ester is replaced with 17.4 g (0.1 mol)of acetoacetic acid-(2-ethoxyethyl) ester, there is obtained the1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylicacid-di-(2'-ethoxyethyl) ester.

    ______________________________________                                        yield:       12.7 g (68% of theory)                                           melting point:                                                                             97-100° C.                                                analysis:    % C         % H         % N                                      found:       59.5        8.0         4.0                                      calculated:  59.8        8.0         4.1                                      ______________________________________                                    

APPLICATION EXAMPLES Testing for thermostability

A dry mixture consisting of 100 parts of S-PVC (K value 58), 4 parts ofepoxidised soybean oil, 0.2 part of montan wax, 5 parts of MBS*(modifying agent), 2 parts of PMMA* (processing auxiliary) and thedihydropyridinecarboxylic acid ester and metal-containing stabiliser inthe amounts given in the following Table in % (relative to the totalcomposition) is rolled on a roll mill for 5 minutes at 190° C. Testsheet specimens 0.3 mm in thickness are taken from the rolled sheet.

The sheet specimens are exposed to heat in an oven at 180° C., and every3 minutes the Yellowness Index (YI) according to ASTM D 1925-70 isdetermined on a specimen.

The results are summarised in the following Table.

       Yellowness Index according to ASTM D 1925-70 and Test substances     exposure to heat (min.)  Dihydro-                    pyridinedi-  Metal-     Test carboxylic  containing  3 6  9  12  15  18  21  24 27  30  33 36     39  42  45 No. acid ester %* stabiliser %* min. min. min. min. min. min.     min. min. min. min. min. min. min. min. min.      1 -- -- -- -- 44 >100              2 Example A 1.5 -- -- 11 17 33 63 87     >100 3 Example B 1.5 -- -- 14 20 29 46 67 94 >100 4 -- -- BCM* 0.5 12 23     42 87 >100 5 Example A 1.5 BCM 0.5 11 11 11 11 13 22 34 87 >100 6     Example B 1.5 BCM 0.5 12 13 13 14 18 23 31 54 >100 7 -- -- MTS* 0.2 13     22 44 62 75 95 >100 8 Example A 1.5 MTS 0.2 12 13 14 16 18 22 27 33 47     59 92 >100 9 Example B 1.5 MTS 0.2 13 16 17 18 19 21 23 24 25 29 32 42     57 >100 10 -- -- BTS* 0.2 6 10 16 20 29 39 49 62 69 77 88 91 98 >100 11     Example A 1.5 BTS 0.2 11 11 11 11 15 17 19 25 31 46 70 88 >100 12     Example B 1.5 BTS 0.2 12 13 13 15 16 19 21 23 27 29 37 45 66 79 90 13 --     -- DBTM* 0.2 37 86 >100 14 Example A 1.5 DBTM 0.2 12 13 17 23 27 34 57     91 >100 15 Example B 1.5 DBTM 0.2 14 17 20 26 32 42 53 66 87 > 100 16     Example E 1.5 -- -- 19 34 67 100 17 Example E 1.5 MTS 0.2 13 13 15 17 21     25 31 36 41 48     *% = relative to the total composition     *BCM = pulverulent stabiliser, mixture of Ba and Cdmyristinate     *BTS = butylthiostannic acid (C.sub.4 H.sub.9 SnS.sub.1.5).sub.n     *MTS = monobutyltin stabiliser of the formula     ##STR6##     ##STR7##

We claim:
 1. A stabilized composition which comprises(a) achlorine-containing thermoplastic polymer, and (b) from 0.5 to 2.5percent by weight, relative to the total composition, of a compound offormula I ##STR8## in which R is branched-chain or straight-chain C₁-C₂₀ alkyl, X is sulfur, and p denotes the numbers 1-8 inclusive.
 2. Acomposition according to claim 1 which additionally contains from 0.05to 1.5 percent by weight, relative to the total composition, of ametal-containing stabilizer selected from the group consisting of theBa/Cd carboxylates, Ba/Zn carboxylates, Ba/Cd/Zn carboxylates, organotinmercaptides, organotin maleates and mixtures thereof.
 3. A compositionaccording to claim 1 which additionally contains a light stabilizer. 4.A composition according to claim 1 wherein the chlorine-containingthermoplastic polymer is a polymer derived from vinyl chloride.
 5. Acomposition according to claim 4 which also contains a plasticizer.
 6. Acomposition according to claim 4 wherein the polymer is rigid poly(vinylchloride).
 7. A composition according to claim 1 wherein the compound offormula I is ##STR9##
 8. A stabilizer mixture consisting of(a) acompound of formula I ##STR10## in which R is branched-chain orstraight-chain C₁ -C₂₀ alkyl, X is sulphur, and p denotes the numbers1-8 inclusive, and (b) a metal-containing stabilizer selected from thegroup consisting of the Ba/Cd carboxylates, Ba/Zn carboxylates, Ba/Cd/Zncarboxylates, organotin mercaptides, organotin maleates and mixturesthereof.
 9. A mixture according to claim 8 wherein the compound offormula I is ##STR11## in which p denotes the numbers 1-4 inclusive, andq denotes the numbers 1-11 inclusive.
 10. A mixture according to claim 9where in the compound of formula I p denotes the number 2 or 3, and qdenotes the number
 11. 11. A mixture according to claim 10 wherein thecompound of formula I is ##STR12##
 12. A mixture according to claim 8wherein the metal-containing stabilizer is a Ba/Cd carboxylate, Ba/Zncarboxylate or Ba/Cd/Zn carboxylate.
 13. A mixture according to claim 8wherein the metal-containing stabilizer is an organotin mercaptide ororganotin maleate.